In a display device using non-light emitting optical components, such as a liquid crystal display device, a backlight device is provided behind a display panel such as a liquid crystal display panel for illuminating the display panel. The backlight device generally includes a plurality of fluorescent tubes (e.g., cold cathode tubes) as light sources. To supply currents to the fluorescent tubes, they need to be connected to electrical lines. However, high precision work is required for the connection and the work is time consuming. A configuration of a fluorescent tube disclosed in Patent Document 1 is known as one that aims to improve work efficiency.
The fluorescent tube disclosed in Patent Document 1 includes a lead line extending from an end of the fluorescent tube and a connecting part for making connection with an electrical wire to supply power to the fluorescent tube. The connecting part includes a conductive base sheet and a through hole. One of ends of the base sheet is configured as a first holding portion for holding the electrical wire. The first holing portion is inserted from one of openings of the through hole. The other end of the base sheet is configured as a second holding portion for holding the lead line of the fluorescent tube. The second holding portion is inserted from the other opening of the through hole.
Patent Document 1: Japanese Published Patent Application No. 2006-93011
(Problem to be Solved by the Invention)
During assembly of the fluorescent tube, the lead line (hereinafter referred to as an outer lead) that extends from the end of the fluorescent tube is inserted in the holding portion of the connecting part (hereinafter referred to as a ferrule). The outer lead is a wire that is widely known as a Dumet wire prepared by wrapping a copper layer around a nickel-iron alloy core wire. Ferrules, sizes of fluorescent tubes and assembly machines may vary from one another, respectively. Therefore, when the outer lead is inserted in the holding portion of the ferrule, a tip of the outer lead may hit the edge of the holding portion and not enter into the through hole of the holding portion. Because the outer lead is in a wire shape, it does not have much tolerance to a bending force caused when the tip hits the edge of the holding portion and thus may be deformed.
To reduce occurrence of such a deformation, a diameter of the outer lead may be increased in size to increase the physical strength thereof. However, a larger diameter of the outer lead may increase a level of displacement between the outer lead and a glass tube that is a main body of the fluorescent tube due to a difference in thermal expansion rates thereof. This may damage the glass tube.
Alternatively, a diameter of an insertion hole of the holding portion may be increased so that the outer lead is easily inserted. This may reduce the occurrence of deformation of the outer lead. However, a large gap is present between the outer lead and the inner surface of the holding portion when the outer lead is inserted in the holding portion. As a result, the outer lead cannot be properly held.